Conventionally, in mechanical parts of various machinery apparatuses, substrate storage containers and the like, in order to meet the different demanded properties of plural parts that constitute a product, a technique for obtaining a product of different materials by separately forming plural parts from different materials and assembling these plural parts into one-body structure has been adopted. As a manufacturing method of such products, insert molding and multicolor molding (also called two color molding or double molding) can be mentioned. In the multicolor molding process, two materials are selected and used from the viewpoint of whether the two molding materials can be joined or not (see patent documents 1 and 2)    Patent document 1:
Japanese Patent Application Laid-open 2005-67139    Patent document 2:
Japanese Patent Application Laid-open 2000-12673